The Wieliczka Salt Mine’s Crystal Caverns: are they inhabited? A first entomological assessment

The Crystal Caverns of the Wieliczka Salt Mine, southern Poland, represent a unique subterranean environment formed within Miocene halite deposits and protected as a nature reserve. In this study, 24 adult beetles of the species Niptus hololeucus (Faldermann, 1835) (Coleoptera: Ptinidae) were collected using Barber pitfall traps during controlled field access. The specimens were evenly distributed across two halite-crystal-covered chambers. No larval stages were recorded, which may reflect methodological limitations associated with non-invasive sampling. Microclimatic data indicate a remarkably stable environment, with temperatures averaging 11.3 ± 0.2 °C and relative humidity ranging between 72–75%. Despite the extreme subterranean conditions—characterized by darkness, high salinity, and limited trophic resources—the repeated occurrence of N. hololeucus, a cosmopolitan and synanthropic species also known from rodent nests and other subterranean habitats, suggests ecological tolerance and opportunistic use of underground environments rather than obligate specialization. This study provides the first entomological record from the natural Crystal Caverns of the Wieliczka Salt Mine and contributes baseline data for understanding arthropod occurrence in salt cave systems, emphasizing the need for cautious interpretation and further targeted research under strict conservation constraints.